The uprising that broke out Saturday evening didn't subside until after midnight, after Mayor Tom Barrett and other city leaders appeared at a news conference to plead for calm. Police said three people were arrested, and one officer was hurt by a brick thrown into a squad car.

The triggering event came Saturday afternoon, when a man fleeing police after a traffic stop was shot and killed. Police said the man was armed, but it wasn't clear whether he was pointing the gun or aiming it at officers. Barrett said the man was hit twice, in the chest and arm.

At a news conference on Sunday, authorities identified the man as 23-year-old Sylville Smith. Police Chief Ed Flynn said Smith had a "lengthy arrest record" with the Milwaukee Police Department.The protesters were largely black, and Alderman Khalif Rainey — who represents the district — said early Sunday morning that the city's black residents are "tired of living under this oppression."

"This entire community has sat back and witnessed how Milwaukee, Wisconsin, has become the worst place to live for African-Americans in the entire country," Rainey said at the end of a news conference at which Barrett pleaded for calm. "Now this is a warning cry. Where do we go from here? Where do we go as a community from here?

The anger at shootings by Milwaukee police is not new, and comes as tension between black communities and law enforcement has ramped up across the nation, resulting in protests and the recent killings of officers in Baton Rouge, Louisiana, and Dallas.

Milwaukee was beset by protests and calls for police reform after an officer fatally shot Dontre Hamilton, a mentally ill black man, in 2014. In December, the Justice Department announced it would work with Milwaukee police on reforms. Chief Ed Flynn had asked for what's known as a collaborative reform process after the federal government said it wouldn't pursue criminal civil rights charges against the officer.

Critics said the department should have submitted to a patterns and practices review, as in Ferguson, Missouri, after the fatal shooting of 18-year-old Michael Brown, who was black, by a white police officer in 2014.

The state is investigating the latest shooting in Milwaukee. Barrett said the officer was wearing a body camera.

"We understand the frustration people feel with the police community nationally. ... We have to go through the process of finding justice, but we have to be able to restore order to these neighborhoods," Hamilton said. "Please participate in restoring order to these neighborhoods."

Barrett said the 23-year-old man who died was stopped by police for "suspicious activity." Police said earlier that he was carrying a gun that had been stolen in a March burglary in suburban Waukesha.

"This stop took place because two officers ... saw suspicious activity," the mayor said. "There were 23 rounds in that gun that that officer was staring at. I want to make sure we don't lose any police officers in this community, either."

As many as 100 protesters massed at 44th Street and Auer Avenue between 8 and 9 p.m., surging against a line of 20 to 30 officers. The Milwaukee Journal Sentinel reported that officers got in their cars to leave at one point and some in the crowd started smashing a squad car's windows. Another police car was set on fire. The newspaper reported that one of its reporters was shoved to the ground and punched.

Around 11 p.m., police with shields and helmets moved slowly into the intersection, telling a crowd of about 50 people to disperse. Some threw rocks and other debris at police, who held up their shields. People in the crowd also threw objects at a business a half-block from the intersection. A nearby traffic light was bent over and bus shelters overturned.

The businesses that burned included a BMO Harris bank branch, a BP gas station, an O'Reilly Auto Parts store and a beauty supply store. Firefighters held back from the gas station blaze because of gunshots.

Police said the man who was shot had an arrest record. The 24-year-old officer who shot the man has been placed on administrative duty. The officer has been with the Milwaukee department six years, three as an officer.

The shooting occurred just a few blocks from two fatal shootings Friday and Saturday, part of a violent stretch in the city in which five people died in shootings during a nine-hour stretch.

Assistant Chief Bill Jessup alluded to the violence in discussing the fatal shooting.

"As everyone knows, this was a very, very violent 24 hours in the city of Milwaukee," Jessup told the Journal Sentinel. "Our officers are out here taking risks on behalf of the community and making split-second decisions."